Characterization of the spray velocities from a pressurized metered-dose inhaler.
BACKGROUND
Pressurized metered dose inhalers (pMDIs) are widely used to deliver aerosolized medications to the lungs, most often to relieve the symptoms of asthma. Over the past decade, pMDIs have been modified in several ways to eliminate the use of chlorofluorocarbons in their manufacture while increasing efficacy. Numerical simulations are being used more frequently to predict the flow and deposition of particles at various locations, both inside the respiratory tract as well as in pMDIs and add-on devices. These simulations require detailed information about the spray generated by a pMDI to ensure the validity of their results.


METHODS
This paper presents detailed, spatially resolved velocity measurements of the spray emitted from salbutamol sulfate pMDIs obtained using optically triggered particle image velocimetry (PIV). Instantaneous planar velocity measurements were taken and ensemble-averaged at nine different times during the spray event ranging from 1.3 to 100 msec after a pneumatically controlled actuation.


CONCLUSIONS
The mean spray velocities were shown to be bimodal in time, with two velocity peaks and velocity magnitudes found to be much lower than published data from instantaneous single point measurements. Planar velocity data at each time step were analyzed to produce prescriptive velocity profiles suitable for use in numerical simulations. Spray geometry data are also reported. Statistical comparisons from several thousand individual spray events indicate that there is no significant difference in measured velocity among (1) two brands of pMDI canisters, (2) two pMDIs of the same brand but having different lot numbers, and (3) a full pMDI versus an almost empty pMDI. The addition of a secondary air flow of 30 SLPM (to represent simultaneous inhalation and spray actuation) deflected the spray downward but did not have a significant effect on flow velocity. Further experiments with an added cylindrical spacer revealed that within the spacer, the spray direction and cone angle were altered, although the peak velocities remained similar.
Crosland
Brian Michael
BM
Mechanical and Aerospace Engineering, Carleton University, Ottawa, ON K1S 5B6, Canada.
Johnson
Matthew Ronald
MR
Matida
Edgar Akio
EA
D000280:Administration, Inhalation; D000336:Aerosols; D000420:Albuterol / Q000008:administration & dosage*; D018927:Anti-Asthmatic Agents / Q000008:administration & dosage*; D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D036501:Metered Dose Inhalers; D008962:Models, Theoretical; D009038:Motion; D009716:Numerical Analysis, Computer-Assisted; D011312:Pressure; D015203:Reproducibility of Results; D012212:Rheology; D013997:Time Factors
D000336:Aerosols; D018927:Anti-Asthmatic Agents; D000420:Albuterol